What for Jay McInerney constitutes the good life? Reading his early fiction, you were left in little doubt that to lead a good life you would need to be young, attractive, have at least a million dollars in the bank and a fine apartment in a fashionable neighbourhood of a great metropolis, preferably Manhattan. You would be surrounded by smart and ambitious people just like yourself. You would wear the right labels, know how to negotiate a wine list and have access to a steady supply of cocaine. You would need all of this as well as the energy to party, network and pursue the hard, fast sensation of living a full life in the big city.

It was obvious that McInerney was more than half in love with the material world whose vapidities he sought to satirise; that in all likelihood he would have agreed with the narrator of his debut novel, Bright Lights, Big City, that there was "no goal higher than the pursuit of pleasure".

The model for McInerney has long been F Scott Fitzgerald - the title of this collection of stories alludes to Fitzgerald's fifth and final novel, The Last Tycoon. Fitzgerald was the original bright young thing of American letters, the writer who, especially in his early stories and debut novel, This Side of Paradise, positioned himself as the ideal chronicler of the exuberant frivolities of the Jazz Age, just as McInerney, in Bright Lights and the novels that followed, would become the self-appointed chronicler of the excitement and excesses of the Manhattan high life of the 80s.

It's clear why McInerney would be so admiring of Fitzgerald. Both writers are obsessively interested in wealth and high-born privilege. Both enjoyed immediate and early success with comic debut novels of youthful, romantic confusion. Both writers are, at heart, sentimentalists (though Fitzgerald is more of an elegist, with a greater sense of the tragic). They savour beauty while being tormented by its very transience and fragility.

What ultimately differentiates Fitzgerald from McInerney, apart from the precision and grace of his elevated prose style, is that his vision of the world darkened and changed through personal suffering, so that even before he was 30 he was capable of writing The Great Gatsby, a major theme of which is the corruption of American innocence. His later work, notably the novel Tender Is the Night, with its loose, fragmentary structure, modernist time shifts and streams of consciousness, and the autobiographical story "The Crack Up" have a pathos and complexity unlike anything in McInerney.

Until, that is, McInerney published his seventh and best novel, The Good Life (2006). Set in Manhattan just before, during and after the attacks of 11 September 2001, the novel concerns a group of wealthy friends - the usual lawyers, financiers, film producers and writers - who are in their various ways seeking to find meaning and a greater sense of purpose as they approach middle age, with its attendant disappointments and compromises. Something has been lost from their lives, and, as McInerney writes, they want "to rekindle the romance and fan it back to life".

Then the attacks occur and each character responds to the catastrophe with troubled particularity. What unites them is a sense that nothing can or should be the same again; that this is a moment of definitive rupture; that the easy pleasures of old are no longer affordable. "I think we're witnessing the beginning of the end of the whole idea of the city," reflects Russell Calloway, one of the lead characters, in a moment of crisis.

Calloway: a name that sounds not unlike Nick Carraway, the narrator of The Great Gatsby. The allusions to Fitzgerald continue on through the 12 stories of The Last Bachelor. But also, as in The Good Life, there is again this urgent preoccupation with existential questions of meaning, purpose and authenticity. Indeed, two of the most anguished characters from The Good Life, the thwarted lovers Corrine and Luke, return in "The March", a story set during an anti-war demonstration in New York in 2003 and which serves as a coda to the novel.

McInerney has two distinct registers, the satiric and the nostalgic. Sometimes, the registers collide uneasily, as in the ludicrous "Sleeping With Pigs", in which the wife of a successful Manhattan writer buys a pot-bellied pig and takes to sleeping with it in the marital bed, in protest against her husband's indifference. The set-up is satirical, but the prevailing tone is, curiously, nostalgic, as the narrator strives to recapture those fleeting moments of grace in his life when the world had seemed so full of hope and enchantment.

McInerney's middle-aged sophisticates tend to be married or in long-term relationships and yet they are in revolt against fidelity. In "I Love You, Honey" a film producer is having sex with his girlfriend in her apartment on the morning of the 11 September attacks. His office is close to the Twin Towers but when his panicked wife calls on his mobile, he tells her that everything is just fine, which naturally arouses her suspicion. Later, because of his continued adulteries, she has two abortions to punish her husband for his lies.

In "Everything Is Lost", a woman is trying to organise a surprise party for her boyfriend's 35th birthday. They share a small loft apartment and she realises how difficult it is to do even the smallest things without his knowing. Yet organising the party is the means by which she realises she can live a life apart from him, with its own thrills and secrecies.

Illicit sex and the inevitability of betrayal within relationships are the motors of these stories, written with characteristic easy fluency of style. But McInerney is, like his characters, getting older. Pleasure is still being pursued, but now there is more pain, guilt and anxiety.

The city remains big, but the lights are no longer so bright and alluring. In fact, it is twilight out there and we move through the world of these stories with amusement, but also sad resignation.

• Jason Cowley is editor of the New Statesman. His memoir, The Last Game: Love, Death and Football, is published by Simon & Schuster in April